1. Field of the Invention
The present invention pertains, in general, to a printed circuit board (PCB) including a waveguide, and a method of producing the same. More particularly, the present invention relates to a PCB in which various shapes of waveguides for a large surface are embedded, and a method of producing the same, in which a core layer cured by UV (UV) and a clad layer are coated on the PCB and the core layer is then exposed using an exposing film on which a waveguide pattern is formed. Additionally, the present invention provides a multi-layered PCB including waveguides embedded therein and a method of producing the same, in which a prepreg is interposed between the waveguide-embedded PCBs to conduct a layup of the PCB and a viahole are then formed and copperplated to electrically connect layers constituting the resulting PCB to each other.
2. Description of the Related Art
Generally, a PCB is used as critical parts of electric and electronic products for connecting electronic parts to each other along a circuit pattern designed on a substrate or supporting the electronic parts, and acts as a passive component widely used in home appliances, communication devices, and industrial devices.
In this regard, a method of producing the PCB includes attaching a thin film made of a predetermined metal such as copper to one side of a phenol resin or an epoxy resin dielectric substrate, etching the thin film (the remaining portion of the thin film except for a linear circuit pattern is etched and removed) to form a predetermined circuit, and forming holes through the thin film to mount parts on the substrate.
The PCB may be classified into a single-sided PCB, a double-sided PCB, and a multi-layered PCB according to the number of sides of the PCB in which the circuit pattern is formed. At this time, the higher the number of layers constituting the PCB is, the higher the number of parts mounted on the PCB is. Thus, the multi-layered PCB may be adopted in high precision electronic products. The single-sided PCB includes a phenol resin as the substrate, and is used in products such as a radio, a telephone, or a simple-structured instrument, in which a circuit pattern is not complicated. Additionally, the double-sided PCB includes an epoxy resin as the substrate, and is applied to electronic products such as a color TV, a VTR, and a facsimile, in which a circuit pattern is relatively complicated. Furthermore, the multi-layered PCB means a print wire substrate in which conductive patterns are formed on three or more layers including a surface conductive layer, and in which the layers are separated from each other by dielectric films positioned between the layers. The multi-layered PCB is applied to high precision devices such as computers with 32 bits or more, electronic switchboards, or high performance communication devices.
Meanwhile, a flexible PCB is used in case that a circuit board must be moved because it is applied to automated devices or camcorders, and the circuit board must be bent when parts are mounted on the circuit board.
Currently, a transmission speed of a signal of an electronic device is considered as an important parameter according to advances in computer and communication technologies, thus the precision alignment of impedances between parts and circuit patterns in a high frequency PCB becomes vital.
The high frequency PCB is limited in transmitting a large volume of data at an ultra-high speed because a circuit acting as a transmission medium is made of a conductive metal such as copper. To avoid the above limit, an optical PCB is developed, in which a waveguide with a predetermined size is directly formed on a silicone substrate and the resulting silicone substrate is embedded in a PCB.
In other words, the optical PCB includes the waveguide made of a polymer or a glass fiber embedded therein to transmit and receive a beam acting as a signal therethrough unlike a conventional PCB in which a copper plate is patterned to form an inner layer and an outer layer thereof.
In the optical PCB, an electrical and an optical signal are all used, and the ultra-high data communication is interfaced by the optical signal. Additionally, a copper circuit pattern is formed in an element to convert the optical signal into the electrical signal to store data and to treat the electrical signal, and a glass plate as well as the waveguide is embedded in the optical PCB.
However, in case that the waveguide is formed on the silicone substrate and the resulting silicone substrate is embedded in the PCB to form the optical PCB, the waveguide for a large area cannot be formed and it is difficult to conduct the application through the formation of the circuit due to a size of the silicone substrate of 8 to 12 inches.
Further, in the above case, it is impossible to form various shapes of waveguides in the PCB.
Meanwhile, the optical PCB may be applied to a switch and a transceiver of a communication net, a switch and a server of a data communication, a communication device of the aerospace industry and an avionics, a base station of a mobile telephone of a universal mobile telecommunications system (UMTS), or a backplane and a daughter board used in a mainframe/supercomputer.
Additionally, the rapid increase of use of the Internet and the improvement of the service quality on the Internet led to the increase in a quantity of data treated and transmitted, thus the optical PCB acting as a medium capable of conducting an optical-interfacing is developed to extend a bandwidth and increase a treating speed of the signal. In other words, in the conventional PCB, the optical-interfacing without being affected by the EMS (electro magnetic susceptibility) characteristic is needed because the electrical signal is limited by the EMS characteristic during a high-speed switching at a GHz range of the bandwidth.
However, even though ten years have passed since the optical PCB was developed, a first and a second EOCB (electrical-optical printed circuit board) technology in which a backplane treats a signal in a point-to-point manner against a glass fiber, and a third EOCB technology of an optical signal interfacing using a multi channel manner in which a large quantity of data is simultaneously treated are developed, but a method of producing a multi-layered optical PCB is not yet suggested, in which an element, a waveguide acting as a medium, and a glass fiber are embedded in a PCB.